Generally, such laser scanning apparatuses are well known in the prior art and built for measuring the three-dimensional shape of a surface of an object, e.g. by generating a point cloud representing a plurality of points on the object-surface. Hence, a three-dimensional image of the surface of the object to be measured can be generated.
A conventional three-dimensional imaging apparatus with use of a non-contact sensor includes a shape measurement apparatus for measuring a shape of a surface of an object with use of the non-contact sensor and outputting measured data (JP 3554264), a computer for processing the measured data outputted from the shape measurement apparatus, and a display device for displaying a three-dimensional image of the surface of the object with control of the computer.
FIG. 6 is a schematic diagram of an optical unit of the conventional shape measurement apparatus, which includes a laser diode 111, a beam expander 112, a first mirror 113, a second mirror 114, and a third mirror 115. A light emitted from the laser diode 111 travels the first mirror to the third mirror 113-115 and irradiates the object to be measured. The light reflected from the surface of the object travels the third mirror 115, the second mirror 114, a fourth mirror 116, an imaging lens portion 117, and enters a CCD line sensor portion 118 as the non-contact sensor. In the shape measurement apparatus, a case receiving the optical unit is rotatable about an X-axis and the third mirror 115 is rotatable about a Y-axis to scan the surface of the object with the laser diode 111.
FIG. 7 shows a principle of the three-dimensional imaging apparatus. The light emitted from the laser diode 111 irradiates the surface of the object to be measured and the light reflected from the surface is converged with an imaging lens 117a of the imaging lens portion 117 and imaged onto a line sensor 118a of the CCD line sensor portion 118. An imaging position of the reflected light on the line sensor 118a is outputted from the shape measurement apparatus as the measurement data. The computer calculates the three-dimensional shape of the surface of the object with use of a triangulation method utilized for a distance meter. The line sensor 118a also measures an amount of the reflected light to obtain a contrast information of the surface of the object and generate the three-dimensional image of the object.
FIG. 8 is a block diagram of the three-dimensional imaging apparatus. An electrical control apparatus 150 controls the laser diode 111 and is connected to an encoder 121 to detect angle of rotation of a motor 119 to rotate the third mirror 115. Signals are outputted from the electrical control apparatus 150 to a computer 200. The signals are converted into image signals through a coordinate conversion portion 210 and an image process portion 220 to display the three-dimensional image.
In the three-dimensional imaging apparatus shown in FIG. 8, the encoder 121 is attached to the motor 119 to rotate the third mirror 115. The encoder 121 generates an encoder pulse signal to rotate the third mirror 115 about the Y-axis so that the irradiation position of the laser light is detected. The reflected light from the irradiation position is cumulatively stored as electrical charges in a CCD device of the line sensor 118a of the CCD line sensor portion 118 for a period of time between one encoder pulse signal and a next encoder pulse signal. A total amount of the electrical charges stored in the CCD device for the time interval between the encoder pulse signals is measured as the amount of light reflected from the irradiated position.
The CCD device has a reset timing to discharge the stored electrical charge. When the encoder pulse signal of the encoder 121 is not synchronized with the reset timing of the CCD in the conventional three-dimensional imaging apparatus, as shown in FIG. 9, the total amount of the electrical charge stored in the CCD device does not represent the cumulative electrical charge stored between the encoder pulse signals. Accordingly, the conventional three-dimensional imaging apparatus does not measure the correct amount of light reflected from the irradiation position.